Semiconductor Wafer Gettering via Ultrashort Pulsed Laser
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Solution Overview
Problem
Existing methods for forming a gettering sink inside semiconductor wafers, especially those with diameters of 300 mm or larger, require long-time heat treatments or are difficult to implement due to polishing challenges, leading to increased production costs and potential heavy metal contamination.
Innovation Solution
A method involving the use of a low-power laser to generate a multiphoton absorption process at a specific depth within the wafer, forming a modified portion that acts as a gettering sink without the need for prolonged heat treatment, utilizing an ultrashort pulsed-laser to create an amorphous structure that effectively captures heavy metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long-time heat treatment is applied to form an oxygen precipitation portion inside the semiconductor wafer, then a gettering sink is formed, but the production cost increases and heavy metal contamination occurs
Solution Approach 1:
The patent replaces the thermal field (heat treatment) with an optical field (laser irradiation) to form the gettering sink. By using laser beams to induce multiphoton absorption and create modified portions inside the wafer, the method eliminates the need for long-time heat treatment, thereby preventing heavy metal contamination while still achieving effective gettering sink formation.
Solution Approach 2:
The patent changes the fundamental parameter used for gettering sink formation from thermal energy (heat treatment temperature and time) to optical energy (laser wavelength, intensity, and pulse duration). This parameter change enables precise localization of the modified portion at a given depth position without the side effects of prolonged thermal processing.
2Ease of manufacture
If a high-power laser beam is used to form a modified region for wafer division, then the wafer can be divided, but dislocations and modifications are caused at sites other than the focusing point
Solution Approach 1:
The patent uses ultrashort pulsed laser irradiation instead of continuous high-power laser beams. The pulsed nature of the laser allows energy to be delivered in extremely short bursts (picosecond to femtosecond range), creating modified portions only at the focal point where the intensity threshold for multiphoton absorption is exceeded. This periodic action prevents thermal diffusion and avoids dislocations at non-focal sites.
Solution Approach 2:
The patent applies laser energy at an intensity level that exceeds the threshold for multiphoton absorption only at the focal point, creating a localized modified portion. The energy density is carefully controlled to be sufficient for modification at the focus while remaining below the threshold at surrounding areas, thus achieving precise localization without excessive action at non-target sites.
3Reliability
If a gettering sink is formed on the back face of a large-diameter semiconductor wafer, then heavy metal contamination is suppressed, but it becomes difficult to form the gettering sink since the wafer is polished on both surfaces
Solution Approach 1:
Instead of forming the gettering sink on the back face of the wafer (conventional approach), the patent inverts the approach by forming the modified portion from the front face or side surface using laser irradiation. This allows the gettering sink to be created inside the wafer bulk without requiring back-side polishing or access, making it compatible with large-diameter wafers that are polished on both surfaces.
Solution Approach 2:
The patent replaces the mechanical process of back-face polishing and gettering sink formation with optical field-induced modification. By using laser beams to create the modified portion inside the wafer through multiphoton absorption, the method eliminates the need for mechanical access to the back face, thereby solving the manufacturing difficulty associated with large-diameter wafers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the efficient formation of a gettering sink within semiconductor wafers of large diameters without the need for lengthy heat treatments, effectively suppressing heavy metal contamination and improving imaging device performance.
Implementation Method 1
irradiating a laser beam to either face of a semiconductor wafer so as to fit a focusing position into a given depth position of the semiconductor wafer to generate a multiphoton absorption process only in a specific portion of the semiconductor wafer at the given depth position
Data Source
AI summary
A semiconductor wafer is produced by irradiating a laser beam to either face of a semiconductor wafer so as to fit a focusing position into a given depth position of the semiconductor wafer to generate a multiphoton absorption process only in a specific portion of the semiconductor wafer at the given depth position to thereby form a gettering sink.